Electrically activated emitters such as LEDs or lasers may be utilized to provide white light (e.g., perceived as being white or near-white), and have been investigated as potential replacements for incandescent, fluorescent, and metal halide high intensity discharge lamps. Solid state emitters may have associated filters that alter the color of the light and/or include lumiphoric materials (e.g., phosphors, scintillators, or lumiphoric inks/fluorescent dyes) that absorb a portion of emissions having a first peak wavelength emitted by the emitter and re-emit light having a second peak wavelength that differs from the first peak wavelength. Light perceived as white or near-white may be generated by a combination of red, green, and blue (“RGB”) emitters, or, alternatively, by combined emissions of a blue light emitting diode (“LED”) and a lumiphor such as a yellow phosphor. In the latter case, a portion of the blue LED emissions pass through the phosphor, while another portion of the blue LED emissions is converted to yellow, and the blue and yellow light in combination provide light that is perceived as white. Another approach for producing white light is to stimulate lumiphors of multiple colors with a violet or ultraviolet LED source.
LEDs are commercially available as bare LED chips, or as single-chip or multi-chip LED packages. A LED package may include a substrate or submount and at least one LED chip arranged over the substrate or submount. A LED package may further include one or more of the following features: electrical contacts, protective material such as an encapsulant, a reflector, and a lens or diffuser. Fabrication of a conventional LED package typically entails multiple steps such as formation of a leadframe, molding a package body around the leadframe, adding a reflective material to the package body, mounting LED chips to the leadframe, establishing electrical connections between the leadframe and the LED chips (e.g., by forming wirebonds), providing encapsulant material, lumiphoric material, and/or light dispersing material over the LEDs, and adding or forming a lens. LED chips or LED packages may be used in fabricating lighting devices that often include further reflectors, lenses, and the like.
LED chips and/or LED packages are typically performance tested and “binned” (i.e., sorted) according to ranges of dominant wavelength and brightness. Such binning permits intensity and/or color matching between various LED chips or LED packages for use in a particular product or product line. Performance characteristics of LED chips or LED packages may affect their economic value and/or utilization in saleable products. It would be desirable to reduce differences in performance between different LED chips or LED packages after binning is complete, but it has been impractical to do so.
Potential benefits associated with solid state emitters relative to other light emitting device technologies include increased efficiency, longer service life (with concomitant reduction in maintenance costs), reduced waste heat emissions, reduced size/form factor, and mercury-free construction. Numerous end use applications exist for solid state lighting devices, including (but not limited to) interior and exterior lighting for residential/commercial/industrial/entertainment structures and facilities, interior and exterior lighting for vehicles (including but not limited to automobiles), and street lighting (including lighting for roadways and parking areas). Street lighting represents a particularly desirable end use for solid state lighting technology, since it is difficult and expensive to periodically replace light-emitting components of street lights, and long life of solid state lighting devices dramatically reduces the frequency with which light-emitting components need to be changed relative to emitters embodying other lighting technologies.
In typical street light applications, it is desirable to provide sufficiently even light distribution to meet recommended street light uniformity levels while minimizing spillover of light in undesired directions (i.e., wasted light) and minimizing hot spots that may lead to undesirable visibility, safety, and/or glare problems. A traditional filament-based lamp emits light from a single source (i.e., a bulb), and utilizes shields, reflectors, and/or lenses to point an emitted beam in one or more desired directions. In contrast, when solid state (e.g., LED) lamps are used for street lighting applications, an array of packaged LEDs may be placed (e.g., at different angles) in a luminaire, with light affecting elements such as reflectors, shields, and/or secondary optics typically arranged to direct light emitted by the packaged LEDs to desired locations. The use of multiple light affecting elements for individual LEDs (or groups of LEDs) provides enhanced flexibility in controlling properties (e.g., shape, direction, overlap, etc.) of multiple output beams; however, it can be cumbersome and labor-intensive to provide a large number of light affecting elements in a single luminaire and to match individual light affecting elements to individual solid state emitters. Moreover, the use of primary optics associated with LED packages in conjunction with secondary optics associated such luminaires tends to result in optical losses that slightly reduce light output.
The art continues to seek improved lighting devices and lighting device fabrication methods that address one or more limitations inherent to conventional devices and methods.